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i.fft(1)		    GRASS GIS User's Manual		      i.fft(1)

NAME
       i.fft  -	Fast Fourier Transform (FFT) for image processing.

KEYWORDS
       imagery,	transformation,	Fast Fourier Transform

SYNOPSIS
       i.fft
       i.fft --help
       i.fft  input=name  real=name  imaginary=name   [--overwrite]   [--help]
       [--verbose]  [--quiet]  [--ui]

   Flags:
       --overwrite
	   Allow output	files to overwrite existing files

       --help
	   Print usage summary

       --verbose
	   Verbose module output

       --quiet
	   Quiet module	output

       --ui
	   Force launching GUI dialog

   Parameters:
       input=nameA [required]
	   Name	of input raster	map

       real=nameA [required]
	   Name	for output real	part arrays stored as raster map

       imaginary=nameA [required]
	   Name	for output imaginary part arrays stored	as raster map

DESCRIPTION
       i.fft is	an image processing program based on the FFT  algorithm	 given
       by  Frigo et al.	(1998),	that processes a single	input raster map layer
       (input) and constructs the real and  imaginary  Fourier	components  in
       frequency space.

NOTES
       The  real  and imaginary	components are stored into the real and	imagi-
       nary raster map layers.	In these raster	map layers the	low  frequency
       components  are in the center and the high frequency components are to-
       ward the	edges.	The input need not be square. A	 color	table  is  as-
       signed to the resultant map layer.

       The  current  geographic	 region	 and  mask settings are	respected when
       reading the input file. The presence of nulls or	a mask will  make  the
       resulting fast Fourier transform	invalid.

EXAMPLE
       North Carolina example:
       g.region	raster=lsat7_2002_70
       i.fft input=lsat7_2002_70 real=lsat7_2002_70.real imaginary=lsat7_2002_70.imag
       # set region to resulting FFT output map	(due to	new FFT	coordinate space):
       g.region	raster=lsat7_2002_70.real -p
       d.mon x0
       d.rast lsat7_2002_70.real
       d.rast lsat7_2002_70.imag

REFERENCES
	   o   M.  Frigo and S.	G. Johnson (1998): "FFTW: An Adaptive Software
	       Architecture for	the FFT". See www.FFTW.org: FFTW is a  C  sub-
	       routine	library	 for  computing	the Discrete Fourier Transform
	       (DFT) in	one or more dimensions,	of both	real and complex data,
	       and of arbitrary	input size.

	   o   John  A.	Richards, 1986.	Remote Sensing Digital Image Analysis,
	       Springer-Verlag.

	   o   Personal	communication, between program author and Ali R. Vali,
	       Space Research Center, University of Texas, Austin, 1990.

SEE ALSO
	i.cca, g.gui.iclass, i.ifft, i.pca

AUTHOR
       David Satnik, GIS Laboratory, Central Washington	University
       Glynn Clements (FFTW support)

SOURCE CODE
       Available at: i.fft source code (history)

       Main  index | Imagery index | Topics index | Keywords index | Graphical
       index | Full index

       A(C) 2003-2020 GRASS Development	Team, GRASS GIS	7.8.3 Reference	Manual

GRASS 7.8.3							      i.fft(1)

NAME | KEYWORDS | SYNOPSIS | DESCRIPTION | NOTES | EXAMPLE | REFERENCES | SEE ALSO | AUTHOR | SOURCE CODE

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